I dont want to dot-n-dab ... really want studs to make it easier to put up shelving, add electrical sockets etc.
noseall - yes, the plan is to put 2x4 noggins between the roof joists to fix the top plate to. The bottom plate is more of a problem. This is an old Edinburgh flat, so the space between the floor joists is filled with 'deafening' ... a 150 mm layer of old clinker topped with mortar (Victorian sound/thermal insulation) Its supported by thin battens (approx 3" wide) nailed to the underside of the joists.
The floor is to get a 22mm plywood sub-floor, then laminate. So for the bottom plate I had planned to just screw the top plate to the 22mm ply. However I guess I could remove all the deafening from between these two joists only, add 2x4 noggins, and then pack in some sound insulation material.
I like the idea of using the end plate to support the wall (as opposed to the other way around). As noseall says, I could fix it to the top and bottom noggins, as well as the timber lintel. Maybe I could also use construction glue between it and the bricks to stabilize the bricks?
There is a 275mm gap between the door frames. As well as the 90mm end plate (centred), I'll need 3x2's just inside the door frames to support the plasterboard. So 275 - (90+63+63) leaves approx 30mm between the 3x2's and the 4x2. I guess if I plasterboard the partition first, then the plasterboard between the partition and door just needs to span approx 18mm unsupported.
Ian